net/mlx5e: RX, Store SHAMPO header pages in array

Save allocated SHAMPO header pages to an array to which the
mlx5e_dma_info page will point to.

This change is a preparation for introducing mlx5e_frag_page structure
in a downstream patch. There's no new functionality introduced.

Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>